1. Field of the Invention
The invention relates to a PV sub-generator junction box for a photo voltaic (PV) system comprising a plurality of electrical connections for connection to a PV string of one or more PV modules connected in series. The PV sub-generator junction box comprises a sub-generator line terminal for connecting a PV sub-generator line of a remote central PV inverter or for connecting a PV sub-generator line of an intermediate PV generator junction box. The PV sub-generator junction box further comprises an electronic control unit which is connected by a data link to a central control unit of the remote control PV inverter for exchange of data.
The invention further relates to a PV generator junction box having a plurality of sub-generator line terminals for connection to a respective PV sub-generator line of a PV sub-generator junction box. The PV generator junction box includes a main line terminal for connecting a PV main DC voltage line of a remote central PV inverter. The PV generator junction box features at least one main circuit breaker for disconnecting the PV main DC voltage line and/or at least one group circuit breaker for disconnecting the respective PV sub-generator line.
The invention further relates to a PV inverter for a PV system which features at least one sub-generator line terminal for connection to a respective PV sub-generator line or a plurality of PV sub-generator lines and/or for connecting a respective PV main DC voltage line of an intermediate PV generator junction box. The PV inverter features a grid connection for connecting the PV inverter to a power supply network. The PV inverter also features a central control unit for controlling the PV inverter as well as for transmitting data to the plurality of PV sub-generator junction boxes linked to the central control unit via a data link.
Moreover, the invention relates to a PV system with at least one such central PV inverter and with a plurality of such PV sub-generator junction boxes.
2. Description of the Related Art
International patent application WO 02/093655 A1 discloses a photovoltaic system having a plurality of solar modules and a central inverter for feeding power into a public power grid. The solar modules each feature an integrated high-frequency energy transmitter, each of which can be electromagnetically coupled to a high-frequency energy receiver, i.e., on transformational paths. The energy transmitter and the energy receiver are preferably a primary-side and a secondary-side pot coil, able to be coupled over an air gap. The inverter has one or more power cables on which the energy receivers are arranged distributed along the power cable. The energy receivers feed in parallel into the power cable with a DC voltage if a solar module with an energy transmitter is connected to these modules. For voltage regulation of the DC voltage present on the power cable the inverter has a measurement device and a control device, with the voltage being regulated by corresponding activation of an H bridge of the inverter. The inverter also includes a circuit for data communication for receiving data over the power cable. In addition, the photovoltaic system disclosed in WO 02/093655 A1 includes a data bus for data transport. Here, the data transmission can be based on high-frequency electromagnetic coupling. Data is transported between the energy transmitters and the energy receivers.
US 2004/0167676 A1 discloses a method and a device for controlling and managing current generators. Here, the device sends a request over the Internet to the respective current generator as to how much electrical power these are currently generating and feeding into the power supply network. The respective current generators return an appropriate power figure over the Internet. FIG. 3 of US 2004/0167676 discloses a current generator which has a first power line modem. Here, the current generator is plugged by a conventional power grid cable into a socket for electrical feed into a public power grid. The socket and a second power line modem connected to the Internet are installed in a house or the like. The second power line forwards requests received over the Internet to the first power line modem and returns power information obtained to the requesting device.
German publication DE 198 59 732 A1 discloses a method for data transmission between a photovoltaic system with at least one solar module and with a central unit. Here, the central unit can be located in a meter box, for example. The data is transmitted between the at least one solar module and a central unit alternately with the energy generated by the at least one solar module. In the disclosed photovoltaic system, the inverters are already integrated into the solar module. As a result, the respective solar module can be connected directly to the public power supply network. Here, data is only transmitted between the respective inverters and the central unit if the power feed has been interrupted beforehand by operating a switch. By addressing the solar modules, the respective operating data of the solar modules can be interrogated by a computer.
International patent application WO 03/071655 A1 discloses that local energy generating systems, such as PV systems, multiply feed into a high-voltage energy supply network in parallel over a local network and a low voltage local network transformer. Here, the energy generation system includes a load breaker on its load side by which the respective energy supply system can be disconnected from the local network. To monitor the local energy supply systems for overload states or network faults, WO 03/071655 explains that the amplitudes and the frequency of the chained low voltages are measured on the three-phase low-voltage side of the local network transformer. The measured values that are determined are transmitted as digitally-coded data signals over the local network to all energy generation systems. On the load side, the amplitude and the frequency of the three-phase output voltage are likewise measured and compared with the measured values transmitted over the local network as data signals. FIG. 5 of this publication discloses a measurement receiver for receiving measurement data by a power line modem over the three-phase local network of a public power grid. The measurement receiver is connected on the network side to an inverter of the respective energy generation system.
Known photo voltaic PV systems or also solar arrays mostly comprise a central PV inverter and a plurality of series-connected PV modules. Typically around 10 to 20 PV modules are connected in series into a PV string to achieve a useful array voltage for the PV inverter of around 1,000 V. The PV inverter converts the input DC voltage into a single-phase grid voltage, preferably into a three-phase grid voltage for feeding into the power supply grid.
To minimize power losses the PV inverter is typically arranged in the center of the PV system. The PV modules are preferably arranged in the shape of a star around the PV inverter. There can also be a number of PV inverters. With PV systems with a maximum feed-in power of more than 100 KW, especially of more than 1 MW, there is a plurality of PV sub-generator junction boxes which, on the one hand, are each connected through a PV sub-generator line to the central PV inverter and which, on the other hand, are each connected to a plurality of PV modules connected in series into a PV string. Typically a few strings of PV modules, such as eight, are connected to a PV sub-generator junction box.
With especially large PV systems having an electrical feed power of several Megawatts, further PV generator junction boxes can be connected between the many PV sub-generator junction boxes and the central PV generator junction box. A number of PV sub-generator junction boxes can branch off from such a PV generator junction box. The number of PV sub-generator junction boxes typically ranges between 16 and 100.
A PV sub-generator junction box includes a plurality of electrical terminals for connecting the many PV string lines. The ends of the respective PV string lines can be placed on and attached to the terminals. Furthermore, the PV sub-generator junction box typically features a sub-generator line terminal for connecting a PV sub-generator line having a cable diameter which is a multiple thicker than the cable diameter of a PV string line.
Also known from the prior art are PV sub-generator junction boxes featuring an electronic control unit, i.e., a current detection and monitoring unit. Such control units typically feature a processor or microcontroller to transfer locally-recorded data, such as string current measurement values, array voltage measurement values, temperature measurement values or switching or auxiliary contact signals, to a central control unit of the PV inverter for higher-level open-loop and closed-loop control. In the reverse direction of the respective control unit, a PV sub-generator junction box can receive control data from the central control unit of the PV inverter in order, for example, to be able to activate actuators for solar adjustment of the PV modules or switching means, such as contactors.
The plurality of PV sub-generator junction boxes results in a plurality of signal or data lines, i.e., a plurality of bus lines having to be routed from the central PV inverter to the respective PV sub-generator junction box. It is frequently the case that the signal or data lines usually laid jointly with the PV sub-generator lines in a cable duct demand significantly more space than the PV sub-generator lines themselves. Laying the cables for such a PV system is accordingly cost-intensive, tedious and complex.
A known solution to this problem is to provide a wireless data connection, i.e., between the central PV inverter and the respective PV sub-generator junction box. Because of the screening effect of the PV modules, such data connections are extremely uncertain.